Means for determining the carrier frequency using a pseudo-random number generating device are known in the prior art. Pseudo-random number generation is based, inter alia, on a time interval of a sequence of consecutive time intervals. These pseudo-random numbers then serve to determine the carrier frequency to be used, by establishing a correspondence, by means of a table, between the pseudo-random number and a carrier frequency.
A system is known which defines a set of independent spectrum-spreading sub-bands for each signal, with separate and different carriers for each signal. This system prevents interferences between the two signals, since each spectrum-spreading sub-band is used by one signal only. However, this complete separation of the two spectrum-spreading sub-bands used by the two signals reduces the efficiency of the signal by a factor corresponding to the ratio between the spreading of the total spectrum-spreading band used by the two signals and the spreading of the sub-band used by one signal. This is due to the spectrum-spreading processing gains through frequency hopping. In the case where the total band is shared in two identical spreading sub-bands, the efficiency of the signal will be reduced by a factor of two, i.e. 3 dB.
A system implementing the same means for determining the frequency for the two signals is also known. The means for determining the frequency then comprises two carrier frequency tables, the first relating a pseudo-random number with the carrier frequency of the first signal, and the second relating a pseudo-random number with the carrier frequency of the second signal. The correspondence tables are implemented so that the carrier frequencies of the first and second signals are different for the same pseudo-random number. However, if the time intervals of the sequences used by the two signals are not of identical durations, the pseudo-random numbers generated are not identical for both signals. The same frequency therefore risks being used simultaneously by both signals. This solution therefore presents the disadvantage of causing interferences between these two signals.